In certain railway signaling systems, such as, in a broken rail detection system, it is common practice to transmit a sine wave modulated audio frequency signal through the rails to provide protection of trains between head blocks. In such coded carrier track circuits, a transmitter may be connected at one end of a block section to send an encoded signal to a tuned receiver connected to the other end of the block section. The present and chief concern of the subject invention is related to the high power audio frequency transmitters which are utilized in the subject coded signal control system. In the past, the conventional types of audio frequency transmitters were possessed of a number of disadvantages which resulted in inefficient operation. For example, the previous types of high power transmitters consumed an excessive amount of power which necessitated heat sinking and resulted in space and package limitations. Further, existing high power transmitters place an excessive demand on the battery supply voltage source when it is necessary to provide standby power in cases when the primary supply voltage fails. Thus, it would be highly advantageous to improve the efficiency of a high power transmitter so that the power demand is not excessive thereby minimizing the space and package requirements due to the less amount of necessary heat sinking. In addition, an economic advantage is realized due to the reduced power requirements, and the overall cost in manufacturing and installation is materially reduced to the decreased size of a more efficient high power transmitter.